I love Lucid 10.04 LTS 64 bit! I am going to ride it up until April 2013 before upgrading to Precise 12.04 LTS.
The version that you would download now is 10.04.4 which is very stable.
I prefer LTS versions for my main Ubuntu.
Ubuntu Software Center works great although I use sudo apt-get install <package(s)> most of the time.
I never use update manager on any Ubuntu.
For all of my updates I use a script called ud and to get upgrades ud2 entered in terminal.
Someone in this forum showed me this: gedit ~/.bashrc in terminal and paste this toward the bottom where you see aliases.
You have to logout and back in for it to take effect.
# update aliases
alias ud='sudo apt-get update && sudo apt-get upgrade && sudo apt-get clean'
alias ud2='sudo apt-get dist-upgrade'
ud2 will get things that are being held back like a new kernel install and can be entered right after ud.
Update Manager can mess you up sometimes. A friend calls it Update Mangler.